The present invention relates to a device for working the ground comprising a frame with a plurality of standing shafts mounted pivotally thereon, moveable setting means connected with the shafts for collectively pivoting the shafts, each standing shaft being provided on a free end with a lying shaft whereon a disc-shaped body is rotatably mounted, wherein each disc-shaped body has a concave and a convex side, and adjacent disc-shaped bodies are arranged in parallel relationship. Such a device is known from the U.S. Pat. No. 3,675,725.
Such a device (normally known as a disc harrow) is used in agriculture for further working of ploughed earth, for ploughing under seed and manure and/or for weed control. It is of great importance in these workings to keep the working depth, i.e. the depth to which the discs work the ground, substantially unchanged. A disc harrow is generally fixed for this purpose to a so-called three-point lifting device that forms part of a tractor and with which the position of the harrow relative to the tractor, and therewith the working depth, is controlled.
The device according to U.S. Pat. No. 3,675,725 differs from conventional disc harrows wherein the discs are jointly fixed to one continuous shaft in that each disc is arranged on the end of a separate, pivotable standing shaft. This has the great advantage that the angle between the rotating shaft of the discs and the direction of movement of the tractor (the setting angle) can be varied without a continuous shaft having to be swivelled for this purpose through the desired setting angle. Thus prevented is that the discs on one of the outer ends of the harrow are moved far behind the tractor and that their working depth can no longer be properly controlled by the lifting device. In the device according to U.S. Pat. No. 3,675,725 the setting angle of the discs can be varied without the distance between the discs and the tractor changing, whereby, using the lifting device, a virtually constant working depth can be simply maintained.
The disc harrow known from the U.S. Pat. No. 3,675,725 has the great drawback, however, that the standing pivot shafts are placed on the convex side of the discs connected thereto. This results in the danger of earth thrown up by an adjacent disc collecting and clogging between the standing pivot shaft and the disc, whereby the discs can jam.
It should be noted that from the U.S. Pat. No. 2,768,864, a disc harrow is known having a plurality of discs arranged in parallel on a transverse bar, each disc having an associated shank extending downwardly and rearwardly from the transverse bar and being placed on the concave side of the disc. This patent, however, relates to disc harrows having their discs quite close together, whereas the disc harrow of the present invention has its discs relatively far apart, to accommodate their pivotal movement.